The present invention relates to an infrared photodetector sensitive to the wave-lengths in the 0.8 to 1.1 .mu.m range, and having a very short response time.
In the spectral range in question, in the vicinity of 1 .mu.m, several types of photodetectors may be envisaged.
Photodetectors (for example PbS, Tl.sub.2 S) always have response times greater than a microsecond and cannot be considered as fast detectors. The performances of certain photomultipliers are highly satisfactory. For example, photocathodes of the type InAs.sub.0.85 P.sub.0.15 OCs or Ga.sub.1-x IN.sub.x AsOCs have a highly satisfactory quantum yield in the vicinity of 1 .mu.m and a very short rise time, of the order of a nanosecond. However, they present serious practical drawbacks: they are fragile, complex to produce, they require a high bias potential, this rendering them inconvenient to use and increasing their price.
Finally, in the case of photovoltaic detectors, several materials may be envisaged: Ge, Si, InAs, InSb, Hg.sub.1-x Cd.sub.x Te.
French Pat. No. 1,561,967 in particular discloses a large-surface photovoltaic photodetector, sensitive in the 0.8-1.1 .mu.m range, comprising a substrate made of silicon of resistivity greater than 10.sup.3 .OMEGA..cm, a diffusion layer defining a PN junction, a filter placed on the face, close to the junction which is exposed to the radiations in order to stop the radiations of wave length shorter than a predetermined length, and contacts for the application of a bias potential.
More particularly, the detector of the above-mentioned Patent has a maximum sensitivity at around 1.06 .mu.m.
Silicon being sensitive from a wave length of about 0.4 .mu.m, the presence of a predetermined high-pass filter certainly restricts the spectral band of the detector.
Due to the high resistivity of the silicone substrate, the leakage current is indeed weak and substantially constant over a wide bias range. A high inverted bias potential may therefore be applied in order to offset the cut-off wave-length of the silicon and to reduce the junction capacity and consequently the response time.
However, the above-described detector is not suitable for detecting the radiation of the AsGa diodes emitting at 0.95 .mu.m, used in optical telecommunication systems.
It is therefore an object of the present invention to solve such a problem.